1. Field
The invention relates generally to the control of a fluid displacement apparatus, by controlling the volume of fluid displaced or transmitted through such apparatus in response to an external parameter. More specifically, this invention relates to a rotary vane compressor frequently utilized for passenger compartment air conditioning on automobiles. In such compressors, retention of the vanes in their retracted position stops the pumping action. The present invention discloses a control circuit to provide for vane retention in the retracted position to modulate the compressor output in response to changing engine speeds, and cooling loads. It may replace the present clutch mechanism on an automotive air conditioning compressor for complete disengagement of the compressor from the driving means.
2. Prior Art
Control of the output or discharge from a compressor or rotary vane fluid displacement apparatus by control of the vanes has been demonstrated in the art. Methods usually employed to retain or retract these vanes utilize a mechanical clamping device, electromechanical device, control a clutch or use a regulator valve to control the discharge pressure. U.S. Pat. No. 2,696,790 (Crow) discloses a means to control radial movement of the blades from outside the pump utilizing an auxiliary source of hydraulic fluid and a manually operable cam mechanism. Cam mechanism rotation causes longitudinal movement of ring 27 to thus rotate pinions 30. Rotation of pins 30 adjusts rack 60 to control the outward movement of blades B. U.S. Pat. No. 2,175,413 (Sharar) teaches an hydraulic clutch with a slide or rod that is attached to two vanes and which slide is retractable to control the travel of the vanes through a pivot mechanism. An adjustable capacity vane pump is disclosed in U.S. Pat. No. 1,603,437 (S. G. Wingquist). The vanes and vane abutments are radially adjustable and the pump assembly itself comprises two vane pumps. The vanes 14 are actuated by springs 19 and the abutment vanes 20 are radially adjustable by the axial movement of slides 26 along the rotor axis. A continuous spring band to produce an outwardly biasing force on the vanes is taught in U.S. Pat. No. 3,904,327 (Edwards et al.), however, it does not teach vane retention. U.S. Pat. No. 3,137,235 (F. B. Brown) discloses a variable volume rotary pump which varies the pump delivery by moving a ring which defines the peripheral wall of the rotor chamber. U.S. Pat. No. 3,153,384 (Castel et al.) provides a vane type pump in which the vanes are continually pressurized radially at pump pressure, but the rotor chamber wall is shiftable to attain a no pumping capacity by moving pivot rings. In U.S. Pat. No. 3,180,271 (Hartmann) fluid pressure is utilized to hold the vanes extended and controls volume flow by movement of a port ring. This device utilizes both a governor 31 and a volume limit control 43. A means for retaining a pair of vanes in a compressor is illustrated in U.S. Pat. No. 4,050,263 (Adalbert et al.). In this disclosure a locking member engages a vane projection to retain the vanes in the retracted position. The locking member is axially movable along the rotor axis by an electromagnetic means. U.S. Pat. No. 4,132,512 (Roberts) teaches a means of vane retention utilizing a permanent magnet and a change of polarity therein to retain the vanes in the retracted position.